1. Field of the Invention
The present invention relates to a remote control device of an acousto-optic tunable filter used in the wavelength division multiplexed transmission system, an optical transmission system containing an equalizer using the acousto-optic tunable filter, and an optical transmission system containing a optical add/drop multiplexer using the acousto-optic tunable filter.
2. Description of the Related Art
The acousto-optic tunable filter (hereunder, referred to as xe2x80x9cAOTFxe2x80x9d) has been used for a device to build a wavelength division multiplexed transmission system. A gain equalizer, power equalizer, optical add-drop multiplexer (hereunder referred to as xe2x80x9cOADMxe2x80x9d) which utilize the transmittance characteristic of the AOTF have been proposed as devices to build a wavelength division multiplexed transmission system (hereunder, xe2x80x9cwavelength division multiplexedxe2x80x9d is abbreviated by xe2x80x9cWDMxe2x80x9d).
The AOTF is a device in which the acousto-optical effect is applied; and there have been proposed several constructions of the AOTF, however the basic principle of operation is the same.
Let us take an AOTF 30xe2x80x2 shown in FIG. 25 as an example of the construction.
As shown in FIG. 25, the AOTF 30xe2x80x2 is constructed to comprise two input ports (PI) 01, 02 and two output ports (PO) 01xe2x80x2, 02xe2x80x2, a transducer 30xe2x80x2-1 placed on a flat substrate, an absorber 30xe2x80x2-2, a highly concentrated Ti diffusion region 30xe2x80x2-3, and an optical waveguide 30xe2x80x2-4 and the like.
In the construction shown in FIG. 25, giving an RF (radio frequency) signal to the transducer 30xe2x80x2-1 through a control port 30xe2x80x2-7 excites the transducer 30xe2x80x2-1 to generate a surface acoustic wave (hereunder, xe2x80x9csurface acoustic wavexe2x80x9d is simply referred to as xe2x80x9cSAWxe2x80x9d). This SAW propagates through the SAW cladding layer to be absorbed by the SAW absorber 30xe2x80x2-2.
On the other hand, a light signal comes in through the optical input port (PI) 01 to be polarized by a PBS (polarized beam splitter) 30xe2x80x2-5 and split into two optical waveguides. The SAW and the light signal are superposed to interfere with each other, and only a light signal of a part of wavelength is polarized selectively.
The light signal of the wavelength polarized is polarized and separated by a PBS 30xe2x80x2-6 on the output. The light signal split by the PBS 30xe2x80x2-6 goes out from the optical output port (PO) 02xe2x80x2, and the rest goes out from the optical output port (PO) 01xe2x80x2. The wavelength of the light signal polarized is in one-to-one correspondence with the frequency of the RF signal, namely, the SAW frequency, under a constant temperature. That is, varying the frequency of the RF signal makes it possible to select a wavelength of a light signal going out through the output ports (PO) 01xe2x80x2, 02xe2x80x2.
Utilizing this property, if an RF signal of a specific frequency is inputted through the control port 30xe2x80x2-7 where a WDM signal containing light signals having different wavelengths to each other comes in through the input port (PI) 01, the AOTF 30xe2x80x2 will output a light signal of a desired wavelength through the output port (PO) 02. Serving the outputted light signal as a split light signal of the OADM, the AOTF 30xe2x80x2 can be used as an OADM.
Concretely, when using the AOTF 30xe2x80x2 as an OADM, for example, the input port (PI) 01 is used as the main input port, the input port (PI) 02 as the input port for adding a light signal, the output port (PO) 01xe2x80x2 as the main output port (PO), and the output port (PO) 02xe2x80x2 as the output port for splitting a light signal.
Inputting an RF signal through the control port will simultaneously adds/splits a light signal of the wavelength corresponding to the frequency of the inputted RF signal. And, to simultaneously input a plurality of RF signals having different frequencies will select the light signals of a plurality of wavelengths corresponding to these RF signals. That is, the AOTF 30xe2x80x2 is very effective as an OADM filter that is able to simultaneously select light signals of plural and arbitrary wavelengths.
And, the AOTF 30xe2x80x2 is also effective as an optical power equalizer or an optical gain equalizer. When the AOTF 30xe2x80x2 is used as the foregoing application, either one of the two output ports (PO) 01xe2x80x2, 02xe2x80x2 is only needed to be used.
Further, the AOTF 30xe2x80x2 will achieve a variable optical filter that is able to freely vary the transmittance characteristic (transmitted quantity/stopped quantity) of a light signal by varying the power of an inputted RF signal.
In comparison to an optical filter of the fixed wavelength type, the AOTF 30xe2x80x2 is flexible in the choice of wavelengths, and the transmittance characteristic can be made variable as mentioned above.
Accordingly, a WDM transmission system 100xe2x80x2 using the AOTF 30xe2x80x2 can be made up, as shown in FIG. 26. In the WDM transmission system 100xe2x80x2 shown here, the AOTF 30xe2x80x2 is placed on the transmission line through which a WDM light signal propagates between an optical main signal transmitter 11 and an optical main signal receiver 21. And, a device 30xe2x80x2A containing the AOTF 30xe2x80x2 is comprised of an RF signal source 31xe2x80x2 and a control/drive circuit 32xe2x80x2. The device 30xe2x80x2A containing the AOTF 30xe2x80x2 can be used as an optical equalizing device, an OADM, or the like.
In the device 30xe2x80x2A containing the AOTF 30xe2x80x2 having such a construction, the AOTF 30xe2x80x2 operates on the basis of the RF signal outputted by the RF signal source 31xe2x80x2 that is equipped in the same place as the AOTF 30xe2x80x2.
However, if the RF signal source 31xe2x80x2 is installed in the same place as the AOTF 30xe2x80x2 so as to output a desired RF signal to the AOTF 30xe2x80x2 which is used for an optical equalizing device or the like, it will enlarge the scale of the device; and if the AOTF 30xe2x80x2 is used in the transmission line in such a condition, it will increase the power consumption, which is a problem.
Further, if a plurality of the devices 30xe2x80x2A using the AOTFs 30xe2x80x2 are installed in the transmission line, the scale of the devices and the power consumption are further increased, and the maintenance of these devices require more manpower, which is also a problem.
Further, to install the RF signal source 31xe2x80x2 and the control/drive circuit 32xe2x80x2 in the same place as the AOTF 30xe2x80x2 will invite a possibility of disturbances in the electronic circuit of the control/drive circuit 32xe2x80x2 to cause crosstalks, which is another problem.
The present invention has been made in view of the foregoing problems, and an object of the present invention is to provide a remote control device of an AOTF, whereby an RF signal source for controlling the AOTF can be installed separately from the AOTF and a device containing the AOTF can be controlled from a remote place, and a WDM transmission system that contains such a device.
In order to accomplish the foregoing object, the remote control device of the acousto-optic tunable filter according to the invention is characterized by comprising: an acousto-optic tunable filter interpolated in an optical transmission line, capable of controlling an output state of an input light signal by being supplied with a surface acoustic wave control signal through a control port; a surface acoustic wave control signal source to generate the surface acoustic wave control signal, which is provided at a remote place from the acousto-optic tunable filter; and a control unit that receives an information of the surface acoustic wave control signal from the surface acoustic wave control signal source through remote transmission means, and supplies the surface acoustic wave control signal to the control port of the acousto-optic tunable filter.
Therefore, according to the remote control device of the acousto-optic tunable filter relating to the invention, it is possible to remotely control the acousto-optic tunable filter by the surface acoustic wave control signal generated by the surface acoustic wave control signal source which is remotely located from the acousto-optic tunable filter, whereby the scale of the peripheral equipment of the acousto-optic tunable filter disposed in the optical transmission line, and the power consumption thereof can be reduced, which is advantageous. Further, the surface acoustic wave control signal source is electrically separated from the control unit, which makes it possible to reduce crosstalks to cause disturbances in electronic circuits, which is also advantageous.
Further, the remote control device of the acousto-optic tunable filter according to the invention is characterized by comprising: a first acousto-optic tunable filter interpolated in an upward optical transmission line, capable of controlling an output state of an upward input light signal by being supplied with a first surface acoustic wave control signal through a first control port; a second acousto-optic tunable filter interpolated in a downward optical transmission line, capable of controlling an output state of a downward input light signal by being supplied with a second surface acoustic wave control signal through a second control port; surface acoustic wave control signal sources to generate the first and second surface acoustic wave control signals, which are provided at a remote place from the first and second acousto-optic tunable filters; and control units that receive information of the first and second surface acoustic wave control signals from the surface acoustic wave control signal sources through remote transmission means, and supply the first and the second surface acoustic wave control signal to the first and the second control port, respectively, of the first and second acousto-optic tunable filters.
Therefore, according to the remote control device of the acousto-optic tunable filter relating to the invention, it is possible to remotely control the acousto-optic tunable filter by the surface acoustic wave control signal generated by the surface acoustic wave control signal source which is remotely located from the acousto-optic tunable filter, whereby the scale of the peripheral equipment of the acousto-optic tunable filter disposed in the optical transmission line, and the power consumption thereof can be reduced, which is advantageous. Further, the surface acoustic wave control signal source is electrically separated from the control unit, which makes it possible to reduce crosstalks to cause disturbances in electronic circuits, which is also advantageous.
Further, the remote control device of the acousto-optic tunable filter according to the invention is characterized by comprising: a first acousto-optic tunable filter interpolated in an upward optical transmission line, capable of controlling an output state of an upward input light signal by being supplied with a surface acoustic wave control signal through a first control port; a second acousto-optic tunable filter interpolated in a downward optical transmission line, capable of controlling an output state of a downward input light signal by being supplied with the surface acoustic wave control signal through a second control port; a third acousto-optic tunable filter interpolated in the downstream of the second acousto-optic tunable filter in the downward optical transmission line, capable of controlling an output state of the downward input light signal outputted from the second acousto-optic tunable filter by being supplied with the surface acoustic wave control signal through a third control port; a surface acoustic wave control signal source to generate the surface acoustic wave control signal, which is provided at a remote place from the first, second, and third acousto-optic tunable filters; and a control unit that receives an information of the surface acoustic wave control signal from the surface acoustic wave control signal source through remote transmission means, and supplies the surface acoustic wave control signal to the first, second, and third control ports of the first, second, and third acousto-optic tunable filters.
Therefore, according to the remote control device of the acousto-optic tunable filter relating to the invention, it is possible to remotely control the first, second, and third acousto-optic tunable filters by the surface acoustic wave control signal generated by the surface acoustic wave control signal source which is remotely located from the first, second, and third acousto-optic tunable filters, whereby the scale of the peripheral equipment of the first, second, and third acousto-optic tunable filters disposed in the optical transmission line, and the power consumption thereof can be reduced, which is advantageous. Further, the surface acoustic wave control signal source is electrically separated from the control unit, which makes it possible to reduce crosstalks to cause disturbances in electronic circuits, which is also advantageous.
Further, the optical transmission system containing equalizers using acousto-optic tunable filters according to the invention is characterized in that: a plurality of equalizers are cascaded in the optical transmission line installed between a light signal transmit terminal and a light signal receive terminal, and the equalizers are comprised of the acousto-optic tunable filters capable of controlling output states of input light signals by being supplied with surface acoustic wave control signals through control ports; the optical transmission system contains, at remote places from the acousto-optic tunable filters, surface acoustic wave control signal sources to generate the surface acoustic wave control signals and surface acoustic wave light control signal transmitting units that output to convert the surface acoustic wave control signals from the surface acoustic wave control signal sources into surface acoustic wave light control signals; and each of the equalizers is provided with a control unit including a receiving unit that receives the surface acoustic wave light control signal from the surface acoustic wave light control signal transmitting unit through the optical transmission line and converts the surface acoustic wave light control signal into the surface acoustic wave control signal, and a driving unit that supplies the surface acoustic wave control signal received by the receiving unit to the control port of the acousto-optic tunable filter.
Therefore, according to the optical transmission system containing equalizers using acousto-optic tunable filters relating to the invention, it is possible to build an optical transmission system capable of maintaining the transmission characteristic of the wavelength division multiplexed signal in a good condition, which is advantageous. And in addition, it is possible to remotely control the acousto-optic tunable filter by the surface acoustic wave control signal generated by the surface acoustic wave control signal source which is remotely located from the acousto-optic tunable filter, whereby the scale of the peripheral equipment of the acousto-optic tunable filter disposed in the optical transmission line, and the power consumption thereof can be reduced, which is advantageous. Further, the surface acoustic wave control signal source is electrically separated from the control unit, which makes it possible to reduce crosstalks to cause disturbances in electronic circuits, which is also advantageous.
Further, the optical transmission system containing a optical add/drop multiplexer using an acousto-optic tunable filter according to the invention is characterized in that: the optical add/drop multiplexer is connected through optical transmission lines between a light signal transmit terminal, a light signal receive terminal, and a branch terminal, and is comprised of the acousto-optic tunable filter capable of controlling an output state of an input light signal by being supplied with a surface acoustic wave control signal through a control port; the optical transmission system contains, at a remote place from the acousto-optic tunable filter, a surface acoustic wave control signal source to generate the surface acoustic wave control signal and a surface acoustic wave light control signal transmitting unit that outputs to convert the surface acoustic wave control signal from the surface acoustic wave control signal source into a surface acoustic wave light control signal; and the optical add/drop multiplexer is provided with a control unit including a receiving unit that receives the surface acoustic wave light control signal from the surface acoustic wave light control signal transmitting unit through the optical transmission line and converts the surface acoustic wave light control signal into the surface acoustic wave control signal, and a driving unit that supplies the surface acoustic wave control signal received by the receiving unit to the control port of the acousto-optic tunable filter.
Therefore, according to the optical transmission system containing a optical add/drop multiplexer using an acousto-optic tunable filter relating to the invention, it is possible to remotely control the acousto-optic tunable filter by the surface acoustic wave control signal generated by the surface acoustic wave control signal source which is remotely located from the acousto-optic tunable filter, whereby the scale of the peripheral equipment of the acousto-optic tunable filter disposed in the optical transmission line, and the power consumption thereof can be reduced, which is advantageous. Further, the surface acoustic wave control signal source is electrically separated from the control unit, which makes it possible to reduce crosstalks to cause disturbances in electronic circuits, which is also advantageous. And in addition, it is also possible to achieve a universal OADM-Branching Unit by using the acousto-optic tunable filter, which in consequence makes it possible to build a wavelength division multiplexed transmission network system having a higher flexibility.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.